In computer networking, the term “multicast” refers to the delivery of a message or information to a group of destination computers simultaneously in a single transmission from the source creating copies automatically in other network elements, such as routers, only when the topology of the network requires it. Multicast is most commonly implemented in PIM multicast, which is often employed in Internet Protocol (IP) applications of streaming media and Internet television. In PIM multicast the implementation of the multicast concept occurs at the PIM routing level, where routers create optimal distribution paths for datagrams sent to a multicast destination address. At the Data Link Layer, multicast describes one-to-many distribution such as Ethernet multicast addressing, Asynchronous Transfer Mode (ATM) point-to-multipoint virtual circuits (P2MP) or Infiniband multicast.
Shortest Path Bridging (SPB) is a transport network protocol that provides logical Ethernet networks on native Ethernet infrastructure using a link state protocol to advertise both topology and logical network membership. Packets are encapsulated at the edge of an SPB network either in mac-in-mac 802.1ah or tagged 802.1Q/802.1ad frames and transported only to other members of the logical network. Unicast and multicast are supported and all routing is on symmetric shortest paths. Many equal cost shortest paths are supported.
Intermediate System To Intermediate System (IS-IS) is a routing protocol designed to move information efficiently within a computer network, a group of physically connected computers or similar devices. ISIS accomplishes this by determining the best route for datagrams through a packet-switched network. The protocol was defined in ISO/IEC 10589:2002 as an international standard within the Open Systems Interconnection (OSI) reference design. Though originally an ISO standard, the IETF republished the protocol as an Internet Standard in RFC 1142. IS-IS has been called the de facto standard for large service provider network backbones.